Electric incandescent lamps

ABSTRACT

A tungsten-halogen cycle electric incandescent lamp contains a solid, partially halogenated, aromatic halide in the fill which dissociates when the lamp is heated to provide halogen to support the regenerative cycle. The aromatic halide may be tri-, tetraor pentabromobenzene and the fill may also include a halophosphonitrile.

O United States Patent 1 1111 3,912,961

Rees et al. Oct. 14, 1975 ELECTRIC INCANDESCENT LAlVIPS [56] References Cited [75] Inventors: John Michael Rees; Vivian Walter UNITED STATES PATENTS Goddard, both of London, England 3,811,063 5/1974 Rees et a1. 313 222 [73] Assignee: Thorn Electrical Industries Limited, I I

London England Przmary Exammer-R. V. Rolmec Assistant ExaminerDarwin R. Hostetter Flled: y 1974 Attorney, Agent, or Firm-Robert F. OConnell [21] App]. No.: 491,675

[57] ABSTRACT [30] Foreign Application Priority Data A tungsten-halogen cycle electric incandescent lamp N 28 1973 U d Ki d 55230 73 contains a solid, partially halogenated, aromatic halide mte ng om 73 67/09 in the fill which dissociates when the lamp is heated to Dec. 11, 1973 Sweden 1 provide halogen to pp the regenerative Cycle The aromatic halide may be tri-, tetraor pentabromo- [52] US. Cl. 313/223, 313/222, 316/20 benzene and the fill may also include a halophos [51] Int. Cl. H01J 61/12 phonitrile [58] Field of Search ..L 313/222, 223; 316/20 12 Claims, 2 Drawing Figures US. Patent Oct. 14, 1975 3,912,961

ELECTRIC INCANDESCENT LAMPS Such lamps have a tungsten filament enclosed within a light-transmitting envelope containing a fill of nonreactive gas, such as N Ar, Kr or Xe, and a small quantity of halogen, for example iodine.

The simplified mechanism of the reactions occurring during operation of such a lamp is that tungsten escaping from the incandescent filament, which would normally diffuse to the bulb wall, reacts with the iodine to form tungsten iodide. When the tungsten iodide diffuses into the high temperature zone surrounding the filament it dissociates, liberating the tungsten and iodine. This regenerative cycle effectively prevents radial diffusion of tungsten, and the bulb wall remains clean throughout life. Consequently, bulb surface area is not important in a lamp where a regenerative cycle is operating and this allows very compact lamps with mechanically strong tubular fused silica envelopes to be used, so permitting filling to a pressure of several atmospheres, which gives improved filament life.

In certain tungsten-halogen lamps where bromine or chlorine is part or whole of the halogen content in the lamp, it is often advantageous to include an additional component, such as hydrogen, which can combine with the halogen in the cold parts of the lamp interior and effectively control the activity of the tungsten-transport cycle. The hydrogen may also reduce or prevent arcing between adjacent components at different electrical potentials. It has been proposed that a convenient method for introducing the halogen and hydrogen is by a gaseous compound, for example HBr, Cll Br or Ch Br. However, we have found that is is difficult to introduce an accurate dose in a gaseous form and have investigated alternative systems based upon a low vapour pressure halogen-containing solid. An alternative system has previously been described in our US. Pat. No. 3,712,701 wherein it is shown that the activity of the tungsten-transport cycle can be controlled by phosphorus, added with the halogen in the form of a halophosphonitrile dissolved in a suitable solvent. In this case the phosphorus also acts as a getter for water vapour and oxygen.

It has now been discovered that the advantages of introducing a halogen as a low vapour pressure solid, and having hydrogen as an arc suppressant can both be realised by employing a solid partially halogenated, aromatic halide as a means of introducing a halogen into tungsten-halogen incandescent lamps. The preferred aromatic halides have a low vapour pressure of not more than 1 X torr at 25C and are introduced into tungstenhalogen incandescent lamps as a solution in a volatile non-polar solvent, such as petroleum-ether (especially 60-80C b.pt), ether and cyclic, aromatic or chlorinated hydrocarbons, e.g. benzene which is removed from the lamp envelope by evacuation or by flushing with a dry non-reactive gas, (e.g. nitrogen).

The following partially brominated aromatic compounds are of particular interest:-

1,2,4 tribromobenzene, m.pt 44, b.pt 275 giving HzBr ratio 1:1

1,2,3 tribromobenzene, m.pt 87, giving I-IzBr ratio 1,3,5 tribromobenzene, m.pt 119, b.pt 271 giving HzBr ratio 1:1

1,2,3,5 tetrabromobenzene, m.pt 98, b.pt 329 giving ratio I-IzBr ratio 1:2

l,2,4,5 tetrabromobenzene, m.pt 180, giving HzBr ratio 1:2 pentabromobenzene, m.pt 293, giving HzBr ratio of 1:5 (m.pt and b.pt are in C).

1,3,5 tribromobenzene and 1,2,4,5 tetrabromobenzene are the preferred isomers of tribromobenzene and tetrabromobenzene, respectively.

The partially halogenated aromatic compounds can be used individually or mixed so as to adjust the HzBr ratio within the range 1:1 to 1:5.

The advantages of the use of solid aromatic halides include accuracy and repeatability of dosing and relative insensitivity to moisture.

Tungsten-halogen lamps in accordance with the invention will now be more fully described by way of example only with reference to the accompanying drawings, in which:-

FIG. 1 shows a single-ended lamp in the course of manufacture; and

FIG. 2 shows a completed single-ended, twin filament, tungsten-halogen lamp.

Referring to the accompanying drawings, like reference numerals indicate similar portions of the lamps.

In each of the lamps shown, there is a quartz envelope 1 surrounding a tungsten filament 2, with lead-in wires 4, which are press-sealed through the ends of the envelope 1, for supplying electrical current to the filament 2. 1

In the lamp shown in FIG. 1 the filament 2 is connected to electrically conductive foils 6 press-sealed within the material of the lamp envelope 1, and the foils 6 are in turn connected to the lead-in wires 4. The envelope 1 has an exhaust tube 7 connected thereto, giving access to the interior of the envelope.

In FIG. 2, a completed lamp. has twin filaments 2 connected through filament supports 8 and foils 6 to the lead-in wires 4, The foils6 are press-sealed within the material of the envelope 1. A shield 9 is attached to one of the filament support '8- adjacent the upper of the two filaments 2'; The filament supports 8 are located relative to one another by insulating bridge 11 through which they pass.

A sealed-off exhaust tube is indicated at 12 at the upper end of the envelope 1.

Examples of methods of making lamps according to the invention will now be described.

EXAMPLE 1 A 12V W single ended automobile lamp of the type shown in FIG. 1 is dosed with tetrabromobenzene by inserting the needle of a hypodermic syringe into the unsealed exhaust tube 7 of the lamp, and injecting 0.025 cm of a solution containing 0.05g of tetrabromobenzene in 100 cm of petroleum-ether (b.pt 80C) into the lamp envelope 1. The solvent is removed by flushing with a stream of dry nitrogen (preferably containing less than 10ppm of water vapour) passed through the exhaust-tube 7, after which the envelope l is exhausted and gas-filled with argon to a pressure of 3.5 atmospheresat room temperature in the usual manner, and the exhaust tube 7 sealed off. On operation of the lamp, or otherwise raising it to a high temperature, the tetrabromobenzene dissociates to yield bromine for supporting the regenerative cycle, together with carbon and hydrogen.

EXAMPLE 2 0.1g

A 12V 60/55W twin filament single ended tungsten halogen automobile lamp of the type shown in FIG. 2 is produced by injecting 0.04 cm of a solution containing 0.1g of tetrabromobenzene in 100 cm of petroleum-ether (b.pt 6080C) into the lamp envelope 1 through the exhaust tube, and after flushing with a stream of dry nitrogen and exhausting, the envelope 1 is inert gas-filled to 3.5 atmospheres pressure with Kr. The exhaust tube is then sealed off, giving the sealedoff portion indicated at 12 in FIG. 2. In this particular example, the hydrogen, which is released when the tetrabromobenzene is dissociated on heating or operating the lamp, is desirable to minimise the risk of arcing between adjacent components at different electrical potentials.

EXAMPLE 3 A further advantage of aromatic halides is that they are compatible with halophosphonitriles (the use of which is described in the above-mentioned US. Pat. No. 3,712,701). A mixture of these can be added to a lamp either as separate solutions or as a mixture in a single solution. This enables the ratio of phosphorus to halogen to be regulated to suit the particular lamp, or a mixture of halogens to be added in accurately controlled proportions. The mixture of a halophosphonitrile and aromatic halide gives'an additional advantage since excess phosphorus will getter water vapour and oxygen impurities.

A 12V 60/55W twin filament single ended tungstenhalogen automobile lamp of the type shown inFIG. 2 is produced as described in Example 2, where a quantity of 0.04 cm of a solution containing 0.09g of tetrabromobenzene and 0.01 of bromophosphonitrile in 100 cm of petroleum-ether (b.pt 6080C) is injected into the lamp envelope 1 and the inert gas-filling is again 3.5 atmospheres pressure of Kr;

We claim:

1. A tungstenhalogen cycle electric incandescent lamp comprising: a light-transmitting, high temperature-resisting envelope; a tungsten filament within said envelope; lead-in wires sealed through said envelope and connected to said filament; and a fill within said envelope capable of supporting a tungsten-halogen regenerative cycle in co-operation with said filament, said fill comprising a non-reactive gas, carbon, hydrogen, and halogen, said carbon hydrogen and halogen having been formed by dissociation of a solid, partially halogenated, aromatic halide within said envelope.

2. A lamp as claimed in claim 1 wherein said carbon, hydrogen and halogen have'been formed by dissociation of a partially halogenated benzene.

3. A lamp as claimed in claim 2 wherein said partially halogenated benzene is a partially brominated benzene.

4. A lamp'as claimed in claim 3 wherein said partially brominated benzene is selected from the group consist ing of tri-, tetraand penta-bromobenzenes.

5. A lamp as claimed in claim 4 wherein said brominated benzene is 1,3,5 tribromobenzene.

6. A lamp as claimed in claim 5 wherein said brominated benzene is 1,2,4,5 tetrabromobenzene.

7. A lamp as claimed in claim 1 wherein said solid aromatic halide has a vapour pressure of at the most 1 X 10 torr at 25C.

8. A lamp as claimed in claim 1 wherein said fill includes a halogen, phosphorus andnitrogen formed by dissociation of a halophosphonitrile within said envelope.

9. A tungsten-halogen cycle electric incandescent lamp comprising: a light-transmitting high temperature-resisting envelope; a tungsten filament within said envelope; lead-in wires sealed through said envelope and connected-to said filament; and a fill within said envelope comprising a non-reactive gas and a solid, partially halogenated, aromatic halide.

10. A method of making a tungsten-halogen cycle electric incandescent lamp comprising the steps of:

providing a light-transmitting high-temperature resisting envelope having an aperture therein, a tungsten filament therewithin, and lead-in wires connected to said filament and sealed therethrough, introducing a normally solid, partially halogenated, aromatic halide into said envelope through said aperture; exhausting said envelope, gas-filling said envelope with a non-reactive gas; sealing said aperture; and raising said envelope to a high temperature sufficient to dissociate said aromatic halide.

11. A method as claimed in claim 10 wherein a solution of a solid aromatic halide in a volatile non-polar solvent is introduced into said envelope, said solvent being volatilised from said envelope before said gasfilling step.

12. A method as claimed in claim 11 wherein said solvent is selected from the group consisting of petroleum-ether; cyclic hydrocarbons; aromatic hydrocarbons and chlorinated hydrocarbons. 

1. A TUNGSTEN-HALOGEN CYCLE ELECTRIC INCANDESENT LAMP COMPRISING: A LIGHT-TRANSMITTING, HIGH TEMPERATURE-RESISTING ENVELOPE: A TUNGSTEN FILAMENT WITHIN SAID ENVELOPE: LEAD-IN WIRES SEALED THROUGH SAID ENVELOPE AND CONNECTED TO SAID FILAMENT: AND A FILL WITHIN SAID ENVELOPE CAPABLE OF SUPPORTING A TUNGSTEN-HALOGEN REGENERATIVE CYCLE IN CO-OPERATION WITH SAID FILAMENT, SAID FILL COMPRISING A NON-REACTIVE GAS, CARBON, HYDROGEN, AND HALOGEN, SAID CARBON HYDROGEN AND HALOGEN HAVING BEEN FORMED BY DISSOCIATION OF A SOLID, PARTIALLY HALOGENATED, AROMATIC HALIDE WITHIN SAID ENVELOPE.
 2. A lamp as claimed in claim 1 wherein said carbon, hydrogen and halogen have been formed by dissociation of a partially halogenated benzene.
 3. A lamp as claimed in claim 2 wherein said partially halogenated benzene is a partially brominated benzene.
 4. A lamp as claimed in claim 3 wherein said partially brominated benzene is selected from the group consisting of tri-, tetra- and penta-bromobenzenes.
 5. A lamp as claimed in claim 4 wherein said brominated benzene is 1,3,5 - tribromobenzene.
 6. A lamp as claimed in claim 5 wherein said brominated benzene is 1,2,4,5 - tetrabromobenzene.
 7. A lamp as claimed in claim 1 wherein said solid aromatic halide has a vapour pressure of at the most 1 X 10 3 torr at 25*C.
 8. A lamp as claimed in claim 1 wherein said fill includes a halogen, phosphorus and nitrogen formed by dissociation of a halophosphonitrile within said envelope.
 9. A tungsten-halogen cycle electric incandescent lamp comprising: a light-transmitting high temperature-resisting envelope; a tungsten filament within said envelope; lead-in wires sealed through said envelope and connected to said filament; and a fill within said envelope comprising a non-reactive gas and a solid, partially halogenated, aromatic halide.
 10. A method of making a tungsten-halogen cycle electric incandescent lamp comprising the steps of: providing a light-transmitting high-temperature resisting envelope having an aperture therein, a tungsten filament therewithin, and lead-in wires connected to said filament and sealed therethrough, introducing a normally solid, partially halogenated, aromatic halide into said envelope through said aperture; exhausting said envelope, gas-filling said envelope with a non-reactive gas; sealing said aperture; and raising said envelope to a high temperature sufficient to dissociate said aromatic halide.
 11. A method as claimed in claim 10 wherein a solution of a solid aromatic halide In a volatile non-polar solvent is introduced into said envelope, said solvent being volatilised from said envelope before said gas-filling step.
 12. A method as claimed in claim 11 wherein said solvent is selected from the group consisting of petroleum-ether; cyclic hydrocarbons; aromatic hydrocarbons and chlorinated hydrocarbons. 